The long-term objectives of the proposed work are to understand the biochemical mechanism(s) of supranutritional Se in chemoprevention and to utilize this information for mechanistic clinical studies. A chemopreventive role of selenium (Se) in cancers has been implicated in several clinical and numerous animal studies but whether Se is effective against tobacco smoke (TS)-induced lung cancers is unknown. Nor is it clear in general on the form(s) of Se that are chemopreventive. Lung cancer is a leading cause of cancer death and TS-induced lung cancer may be on the rise worldwide due to growing smoking habit. Thus, the specific aims of this proposal are: 1) To examine whether dietary Se supplement in the form of selenized yeast (Se-yeast) or its major component selenomethionine (Se-Met) is chemopreventive for mice that have "quit" smoking; 2) To characterize biomarkers of Se action such as apoptotic markers and selenoproteins that have been established in other chemoprevention studies so that Se chemoprevention can be understood better at the molecular level; 3) To investigate whether a synergism exists between Se and other chemopreventive agents such as the glucocorticoid hormone budesonide and retinoid isotretinoin in TS induction of lung cancers. To fulfill these aims, the A/J mice model which is the only animal model for TS-induced lung cancer will be employed. Mice will be pre-exposed to tobacco smoke to induce lung tumors during the recovery phase. The effect of dietary Se-yeast or Se-Met supplement during the recovery phase on tumor incidence and/or multiplicity will be measured to see if Se supplement is effective in reducing tumor formation and if additional Se form(s) in Se-yeast may be active. Major Se metabolites present in Se-yeast in addition to Se-Met will be characterized by a combination of NMR and HPLC coupled to mass spectrometry. The Se action will be characterized both immunocytochemically and in lung extracts by a series of apoptotic markers including cytochrome c release, activation of caspases, production of caspase cleavage products, and DNA fragmentation will be measured, along with the activation of selenoprotein, thioredoxin reductase. These biomarkers are known to be elicited in other Se chemoprevention studies. A similar approach will be used to investigate any interactive effect of Se-yeast supplement and budesonide or isotretinoin administered via inhalation; the latter two agents are also known to cause apoptosis. Biomarker characterization should reveal whether synergism is mediated via apoptosis.